1. Field of the Invention
The present invention relates to an exchange coupling film comprising an antiferromagnetic film and a ferromagnetic film so that the magnetization direction of the ferromagnetic layer is pinned in a predetermined direction by an exchange coupling magnetic field produced between the antiferromagnetic layer and the ferromagnetic layer. Particularly, the present invention relates to an exchange coupling film which produces a large exchange coupling magnetic field, and a magnetoresistive element (a spin valve thin film element or an AMR element) using the exchange coupling magnetic field, and a thin film magnetic head using the magnetoresistive element.
2. Description of the Related Art
A spin valve thin film element is a GMR (giant magnetoresistive) element utilizing a giant magnetoresistive effect, for detecting a recording magnetic field from a recording medium such as a hard disk or the like.
The spin valve thin film element has some advantages that the structure is relatively simple as compared with other GMR elements, and the resistance changes with a weak magnetic field.
The simplest structure of the spin valve thin film element comprises an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic intermediate layer and a free magnetic layer.
The antiferromagnetic layer and the pinned magnetic layer are formed in contact with each other so that the pinned magnetic layer is put into a single domain state and the magnetization direction thereof is pinned in a predetermined direction by an exchange coupling magnetic field produced at the interface between the antiferromagnetic layer and the pinned magnetic layer.
Magnetization of the free magnetic layer is oriented in the direction crossing the magnetization direction of the pinned magnetic layer by bias layers formed on both sides of the free magnetic layer.
The antiferromagnetic layer generally comprises a Fe—Mn (iron-manganese) alloy film, a Ni—Mn (nickel-manganese) alloy film, or a Pt—Mn (platinum-manganese) alloy film. Particularly, the Pt—Mn alloy film has various advantages of the high blocking temperature, excellent corrosion resistance, etc., and thus gets into the spotlight.
The inventors found that even with an antiferromagnetic layer comprising a PtMn alloy film, an exchange coupling magnetic field produced between the antiferromagnetic layer and a pinned magnetic layer cannot be increased depending upon conditions.
With the antiferromagnetic layer comprising a PtMn alloy film, the antiferromagnetic layer is transformed from a disordered lattice to an ordered lattice by heat treatment after the antiferromagnetic layer and the pinned magnetic layer are laminated, thereby producing an exchange coupling magnetic field.
However, it was found that when the interface between the antiferromagnetic layer and the ferromagnetic layer is put into a coherent state in which the atoms of the constituent antiferromagnetic material of the antiferromagnetic layer have one-to-one correspondence with the atoms of the constituent soft magnetic material of the pinned magnetic layer, the antiferromagnetic layer is not appropriately transformed to the ordered lattice, thereby failing to produce a large exchange coupling magnetic field.